Microstructure engineering of yttrium-doped barium zirconate thin films via seed layer technique

Proton conducting yttrium-doped barium zirconate (BZY) thin films have been successfully synthesized by chemical solution deposition (CSD). The seed layer technique is developed to obtain BZY films with different growth orientations, in combination with the layer-by-layer approach. The concentration of the precursor solution for the deposition of the seed layer is the decisive parameter to the final orientations and microstructures of BZY films. In particular, BZY thin films with the preferred (111) and (100) orientations have been fabricated on platinized silicon wafers, which are rarely reported in previous literature results. Meanwhile, the average grains size can be about 230 nm in the plane of the interface. In addition, these films with certain orientations and larger grains are obtained at a, compared to bulk BZY processing, relatively low annealing temperature (950 °C). The different nucleation behavior during the deposition of seed layers has been discussed to explain this relationship between the fabricating processes and final microstructures. For the BZY thin film with (111) orientation, annular dark field imaging in scanning transmission electron microcopy (HADDF-STEM) has been employed to reveal its porous and layered internal microstructure. In addition, proton conductivity of these thin films has been evaluated by electrochemical impedance spectroscopy (EIS) at intermediate temperatures (350–600 °C).